In the continuous slab casting of steel, molten (liquid) steel from a steelmaking ladle is poured indirectly into a casting mold and cast into semi-finished shapes (slabs, blooms, and billets). The semi-finished shape is determined by the casting machine mold that receives the molten steel from a tundish and casts the steel into a steel strand with a molten inner core and an outer surface solidified by cooling as the strand moves downwardly through the mold. The strand is further subjected to secondary cooling upon exiting from the mold until, the entire strand is solidified. The strand is then cut to a desired length.
In the continuous caster, the molten steel, or melt, from the tundish usually flows into the mold through a shroud and submerged entry nozzle (SEN), which is connected to the outlet of the tundish. The SEN discharges the molten metal into the mold to a selected depth below the surface (the “meniscus”) of the melt in the mold. The flow of the molten melt from the tundish is gravity fed by the pressure difference between the liquid levels of the tundish and that of the melt in the mold. The melt flow from the tundish may be controlled by a stopper rod that at least partially blocks the exit port to the shroud, or a slide gate that moves across the outlet port of the tundish to the shroud. As the molten metal enters the mold, the steel solidifies at the water cooled mold walls to form a shell, which is continuously withdrawn at the casting speed to produce the steel strand by oscillation of the mold walls.
In such a continuous slab casting process, the flow of the molten steel into the mold can affect the quality of the cast steel. Since the outlets of the SEN are below the liquid level in the mold, turbulence and other transient changes in the molten steel produce oxide inclusions and gas bubbles, and flow velocities may entrain droplets of molten slag in the cast strand. Also, foreign particles trapped at the meniscus can similarly be entrained in the cast strand and generate surface defects and surface cracks. All of these produce defects in the cast strand, and result in rejection of the product and loss of manufacturing efficiency.
The width of the steel strand exiting the mold is determined substantially by the relative separation and taper angle of opposing faces of the mold. The molten steel in the mold tends to shrink (i.e., pull away from the mold faces) due to cooling as it moves from the top of the mold (e.g., adjacent the SEN) to the bottom exit of the mold. The mold faces are tapered to account for the shrinkage, so that the molten steel moving through the mold may maintain contact with the mold faces. However, this has proved difficult with different steel compositions processed through the same continuous slab caster, which cool at different rates, even with moveable mold walls. Too much taper may increase incidence of surface defects such as longitudinal and transverse cracking and crinkling of the shell, whereas too little taper may enable the shell to bulge. Excessive bulge may cause a breakout in the shell. Control of the mold face reduces product defects, mold damage and breakouts.
A method of continuously casting steel slabs is disclosed for improved control of the mold faces and the melt as the strand moves through the casting mold. The method of continuously casting steel slabs may include steps of                assembling a casting mold for continuous casting of steel slabs comprising a set of laterally movable opposing mold faces;        introducing molten metal into the casting mold;        monitoring the lateral positions of at least one of the opposing mold faces in two vertically spaced locations along the monitored mold face during casting and producing electrical signals indicative of the lateral position of the mold face at the vertically spaced locations;        controlling the position of the monitored mold face at the vertically spaced locations during casting responsive to the electrical signals indicative of the lateral positions of the mold face.        
The method may further comprise monitoring the lateral positions on each of the opposing mold faces in the set in two vertically spaced locations along the mold faces during casting; and controlling the position of each mold face at the vertically spaced locations during casting responsive to the electrical signals indicative of the lateral positions of the mold face.
Alternately, the method of continuously casting steel slabs may include the steps of:                positioning at least one set of laterally movable opposing mold faces of a casting mold with respect to each other in a predefined lateral configuration;        introducing molten metal into the casting mold;        monitoring the lateral positions of each of the opposing mold faces in at least one location along the monitored mold face during casting and producing electrical signals indicative of the lateral positions of the mold faces;        controlling the position of the monitored mold face during casting responsive to the electrical signals indicative of the lateral positions of the mold faces.        
The method may include automatically adjusting the mold faces during casting to maintain the predefined lateral configuration. Additionally, the predefined lateral configuration may include at least one of a distance set point and a taper set point between the opposing mold faces.
Controlling the position of the monitored mold face may include adjusting lateral positions of the opposing mold faces during casting to maintain at least one of a distance set point and a taper set point between said opposing mold faces. Adjusting the lateral positions of the mold faces may be accomplished using at least one actuator selected from the group consisting of hydraulic drives, electrical drives, and mechanical drives and capable of moving the mold face at the vertically spaced locations during casting as desired. Monitoring of the lateral positions may be accomplished using at least one position sensor selected from the group consisting of temposonic transducers, magnetostrictive position sensors, and linear position sensors. Controlling the position of the monitored mold face may be performed automatically or manually.
The method of continuously casting steel slabs may further comprise directing the metal exiting the mold into a support roller assembly, the metal continuing to solidify into a solid metal strand having a width dimension substantially defined by the opposing mold faces, and cutting the solid metal strand across the width dimension to form a solid steel slab having a predetermined length.
In an alternate method of continuously casting steel slabs, the method may include                assembling a casting mold for continuous casting of steel slabs comprising a set of laterally movable opposing mold faces;        introducing molten metal into the casting mold;        monitoring the forces exerted by the molten metal on at least one of the opposing mold faces in two vertically spaced locations along the monitored mold face during casting and producing electrical signals indicative of the forces exerted on the mold face;        controlling the position of the monitored mold face at the vertically spaced locations during casting responsive to the electrical signals indicative of the forces exerted on the mold face.        
The method may further include monitoring the forces on each of the opposing mold faces in the set in two vertically spaced locations along the mold faces during casting; and controlling the position of each mold face at the vertically spaced locations during casting responsive to the electrical signals indicative of the forces exerted on the mold face.
The position of the monitored mold face may be controlled by adjusting lateral positions of the opposing mold faces during casting to maintain a desired force exerted on the mold face. The monitoring of forces may be accomplished using load cells. In one alternate, at least one load cell is in the form of a clevis pin operatively connecting the mold face and an actuator capable of controlling the position of the mold face at one or more vertically spaced locations during casting as desired. Alternately, the load cells may be integrated with actuators capable of controlling the position of the mold faces during casting as desired.
A continuous steel slab caster is disclosed having                an oscillatable slab caster mold capable of receiving molten steel comprising a set of laterally movable opposing mold faces;        at least two position sensors positioned capable of monitoring the lateral positions of at least one of the opposing mold faces in two vertically spaced locations along the monitored mold face during casting and producing electrical signals indicative of the lateral position of the mold face at the vertically spaced locations; and        actuators capable of controlling the position of the monitored mold face at the vertically spaced locations during casting responsive to the electrical signals indicative of the lateral positions of the mold face.        
The steel slab caster may further include a feedback controller and drive assembly capable of causing the actuators to adjust lateral positions of the opposing mold faces during casting responsive to the electrical signals indicative of the lateral position of the mold face in the vertically spaced locations to maintain at least one of a distance set point and a taper set point between the opposing mold faces.
The position sensors may include at least one sensor selected from the group consisting of temposonic transducers, magnetostrictive position sensors, and linear position sensors, and the actuators may include at least one selected from the group consisting of hydraulic drives, electrical drives, or mechanical drives. The opposing movable mold faces may be the narrow faces of the mold.
Alternately, the continuous steel slab caster may include:                an oscillatable slab caster mold capable of receiving molten steel comprising a set of laterally movable opposing mold faces;        force sensors positioned capable of monitoring the forces exerted by the molten metal on at least one of the opposing mold faces in two vertically spaced locations along the monitored mold face during casting and producing electrical signals indicative of the forces exerted on the mold face; and        actuators capable of controlling the position of the monitored mold face at the vertically spaced locations during casting responsive to the electrical signals indicative of the forces exerted on the mold face.        
The slab caster may include a feedback controller and drive assembly capable of causing the actuators to adjust lateral positions of the opposing mold faces responsive to the electrical signals indicative of the forces exerted on the mold face during casting to maintain a desired force.
The force sensors may be load cells. Additionally, the load cells may be in the form of clevis pins positioned between the opposing movable mold faces and the actuators.
The method of continuously casting steel slabs disclosed is more reliable in maintaining contact between the mold faces and the melt as the strand moves through the casting mold.
The method of continuously casting steel slabs may include adjusting the lateral positions of the opposing mold faces in response to generated data to maintain a distance set point or a taper set point, or both, between the opposing mold faces as casting proceeds. In accordance with an embodiment of the present invention, the adjusting of the lateral position of the opposing mold faces is performed automatically.
The monitoring of the lateral positions of the opposing mold faces may be accomplished in at least two vertically spaced locations along both mold moveable faces as casting proceeds. The adjusting of the lateral positions of the opposing moveable mold faces is performed in response to generated data to maintain distance set points between corresponding laterally positioned locations on the opposing mold faces, or to maintain a taper set point of each of the opposing mold faces, or both as casting proceeds.
Adjusting of the opposing mold faces may be accomplished, either manually by an operator or automatically, employing hydraulic, electrical, or mechanical drives, in accordance with a desired embodiment of the present invention. The opposing moveable mold faces may be the narrow faces of the mold. Alternatively, the opposing moveable mold faces may be the broad faces of the mold.
In any case, the monitoring of the positions of the opposing mold faces may be accomplished using at least one of temposonic transducers, magnetostrictive position sensors, or linear position sensors positioned on the mold wall, or on the drive assembly. As a back up, or in the alternative, the sensors may sense the temperature of the cooling water flowing through the mold adjacent the particular mold face location, which decreases as molten metal moves away from the mold face. Such temperature sensing may be used to give a course indication of whether or not the mold faces are properly positioned.
Alternatively or in addition, the sensors may measure the pressures exerted by the molten metal against the mold face, to measure when the surface of the molten metal moves away from the mold face.
In yet another alternate, the continuous steel slab caster may include the following elements:                (a) an oscillatable slab caster mold capable of receiving molten steel and having at least one set of opposing movable mold faces;        (b) at least two sensors adjacent at least one face of the opposing moveable mold faces at vertically spaced locations along the mold face, with each sensor capable of monitoring a lateral position of the adjacent mold face and/or the pressure exerted by the molten metal against the adjacent mold face at the locations, and generating corresponding position and/or pressure data as casting proceeds; and        (c) positioning devices capable of adjusting the opposed movable mold faces in response to the generated data from the vertically spaced locations.        
The steel slab caster may further comprise a feedback controller and drive assembly. The feed back controller is capable of actuating the drive assembly to automatically adjust the lateral position of the opposing movable mold faces in response to the generated data, to maintain a relative distance set point between the opposing mold faces and/or to maintain a taper set point of each of the opposing mold faces as casting proceeds. In accordance with an embodiment of the present invention, the at least one set of opposing moveable mold faces are the narrow faces of the mold.
The sensors may be temposonic transducers, magnetostrictive position sensors, and/or linear position sensors. As a back up, or in the alternative, the sensors may sense the cooling water temperature circulated through the mold adjacent the particular mold face location, which increases as molten metal move away from the mold face.
Alternatively, the method of continuously casting steel slabs may include the following steps:                laterally positioning at least one set of movable opposing mold faces of a slab caster mold with respect to each other in a predefined lateral configuration;        introducing molten steel into the slab caster mold having the at least one set of opposing mold faces;        monitoring the lateral positions of the opposing mold faces and/or pressures exerted by the molten steel against the mold faces in at least two vertically spaced locations on each movable mold face of the opposing mold faces as casting proceeds;        generating data in response to the monitoring; and        adjusting the opposed movable mold faces in response to the generated data at the vertically spaced locations.        
The method of continuously casting steel slabs may further include automatically adjusting at least one of the lateral positions of the opposing mold faces in response to the generated data to maintain the predefined lateral configuration. In accordance with an embodiment of the present invention, the predefined lateral configuration includes a set point relative distance between the opposing mold faces and/or a set point taper angle of each of the opposing mold faces.
The monitoring may be accomplished using temposonic transducers, magnetostrictive position sensors, and/or linear position sensors. The adjusting may be accomplished using hydraulic, electrical, or mechanical drives, and the opposing moveable mold faces may be the narrow faces of the mold.
The method of continuously casting steel slabs further includes directing the molten steel to exit the mold into a support roller assembly such that the molten steel continues to harden into a solid metal strand having a width dimension substantially defined by the distance between the opposing mold faces at the mold exit. The metal strand may be cut across the width dimension to form solid steel slabs of a predetermined length.
These and other advantages and novel features of the present invention, as well as details of illustrated embodiments thereof, will be more fully understood from the following description and drawings.